We report the study of the helicity-driven photocurrents in graphene excited by midinfrared light of a CO2 laser. Illuminating an unbiased monolayer sheet of graphene with circularly polarized radiation generates\char22{} under oblique incidence\char22{}an electric current perpendicular to the plane of incidence, whose sign is reversed by switching the radiation helicity. We show that the current is caused by the interplay of the circular ac Hall effect and the circular photogalvanic effect. By studying the frequency dependence of the current in graphene layers grown on the SiC substrate, we observe that the current exhibits a resonance at frequencies matching the longitudinal optical phonon in SiC.

The current-induced optical activity in a tellurium single crystal has been experimentally investigated in the mid-infrared spectral region. The phenomenological theory of the current-induced optical activity has been considered and the microscopic mechanism of this phenomenon has been described. The dependence of the degree of spin polarization of holes in tellurium on the electric current density has been determined. An approximate analytical expression relating the current-induced optical activity to the degree of spin polarization of holes has been obtained.

The study of spin photocurrents in (110)-grown quantum well structures is reported. The investigated effects comprise the circular photogalvanic effect and so far not observed circular photon drag...

The circular photon drag effect is observed in a bulk semiconductor. The photocurrent caused by a transfer of both translational and angular momenta of light to charge carriers is detected in tellurium in the midinfrared frequency range. Dependencies of the photocurrent on the light polarization and on the incidence angle agree with the symmetry analysis of the circular photon drag effect. Microscopic models of the effect are developed for both intra- and intersubband optical absorption in the valence band of tellurium. The shift contribution to the circular photon drag current is calculated. An observed decrease of the circular photon drag current with the increase of the photon energy is explained by the theory for intersubband optical transitions. Theoretical estimates of the circular photon drag current agree with the experimental data.

We report a fast, room temperature detection scheme for the polarization ellipticity of laser radiation, with a bandwidth that stretches from the infrared to the terahertz range. The device consists of two elements, one in front of the other, that detect the polarization ellipticity and the azimuthal angle of the ellipse. The elements, respectively, utilize the circular photogalvanic effect in a narrow gap semiconductor and the linear photogalvanic effect in a bulk piezoelectric semiconductor. For the former we characterized both a HgTe quantum well and bulk Te, and for the latter, bulk GaAs. In contrast with optical methods we propose is an easy to handle all-electric approach, which is demonstrated by applying a large number of different lasers from low power, continuous wave systems to high power, pulsed sources.

Terahertz radiation emission from an electrically excited AlGaN/GaN heterostructure with a surface metal grating was studied under conditions of two-dimensional (2D) electron heating by the lateral electric field. Intensive peaks related to nonequilibrium 2D plasmons were revealed in the terahertz emission spectra with up to 4 times selective amplification of the radiation emission in the vicinity of 2D plasmon resonance. This selective emission was shown to be frequency-controllable by the grating period. Exact spectral positions of the 2D plasmon resonances were preliminarily experimentally detected with the help of equilibrium transmission spectra measured at various temperatures. The resonance positions are in a satisfactory agreement with the results of theoretical simulation of the transmission spectra performed using a rigorous solution of Maxwell’s equations. The effective temperature of hot 2D electrons was determined by means of $I$ –$V$ characteristics and their analysis using the power balance equation. It was shown that for a given electric field, the effective temperature of nonequilibrium 2D plasmons is close to the hot 2D electron temperature. The work may have applications in GaN-based electrically pumped emitters of terahertz radiation.